The reactor coolant system of a pressurized water reactor must be operated such that the reactor coolant system pressure is maintained below a maximum allowable pressure limit which is based on the fracture properties of the reactor coolant pressure boundary. In addition, the reactor coolant system pressure must be maintained above minimum allowable pressure limits. Presently, control of the reactor coolant pressure is accomplished by developing limit curves of maximum allowable reactor coolant system pressure versus reactor coolant system temperature and then operating the reactor coolant system below the limits shown on the curves. Such limit curves have been developed for both normal reactor coolant system operation and emergency reactor coolant system operation. Typically, these limit curves are developed prior to the plant being placed in operation and are based on conservative operating parameters so that the curves can be applied to all operating conditions. Thus, the curves are typically based on worst-case reactor coolant system material properties, worst-case temperature transients that the reactor coolant system might experience, worst-case reactor coolant pump combinations, reactor coolant density, reactor coolant flow and heat transfer coefficients. By using the worst-case approach, the resulting curves are very conservative and severely limit the operating conditions of the reactor coolant system.
Because of the foregoing, it has become desirable to develop a pressure/temperature system for a nuclear reactor coolant system that is based on actual operating plant conditions rather than worst-case conditions.